Table of Content

10 May 2020, Volume 39 Issue 5

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Temporal and spatial changes and their driving forces of vegetation cover in Horqin Sandy Land in recent 40 years.

LYU Jia-xin, LI Xiu-fen, ZHENG Xiao, NIE Zhe, LIU Si-qiang

2020, 39(5):  1399-1408. 

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Horqin Sandy Land is a key area for the project of desertification prevention and control in China. In recent years, ecological engineering construction, human activities and vegetation growth in this area have been affected by climate change to some extent. Understandingdynamic change of regional vegetation can provide scientific basis for the comprehensive control of the sandy land and reasonable construction of ecological engineering. Consequently, the spatialtemporal variations and their driving factors of NDVI in Horqin Sandy Land were analyzed based on the dataset of NOAA-NDVI and MODIS-NDVI from 1981 to 2015, as well as meteorological and socioeconomic data. The results showed that from 1981 to 2015, NDVI showed a fluctuating increase trend (with a growth rate of 0.00114 a^-1). Spatially, areas with increasing NDVI(accounting for 68.8% area) were mainly located in the southeast margin and part of the central region, while NDVI of the northwest margin of the study area was decreasing. The change process of NDVI in desertification areas of different degrees was first decreased (1981-2000) and then increased (2001-2015), indicating that vegetation destroyed in the early stage was restored in the later stage. Results of driving force analysis showed that precipitation and temperature were the factors driving NDVI changes in some areas of Horqin Sandy Land. Population change and the implementation of ecological engineering drove the spatial-temporal change of vegetation in this region. However, economic development was not a major factor driving vegetation change in this area.

Above and below ground biomass carbon allocation pattern of different plant communities in the alpine grassland of China.

LIU Li, HU Fei-long, YAN Yan, LU Xiao-qiang, LI Xue-hua, LIU Zhi-min

2020, 39(5):  1409-1416. 

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Alpine grassland has unique natural habitats and biological resources. A comprehensive study of alpine grassland would be beneficial to climate change mitigation and grassland restoration. The estimation of carbon storage in alpine grassland biomass was often based on largescale spatial sampling, ignoring community composition and spatial difference of grasslands, which may affect the accuracy of results. The distribution pattern of above and belowground biomass and their contributions to total biomass carbon of 10 main vegetation types in the alpine grassland were analyzed. The results showed that: (1) Biomass carbon of the alpine grassland was 1.53 Pg (1 Pg=10¹⁵ g) within an area of 167.33×10⁶ hm², with above and belowground biomass being 0.19 Pg and 1.34 Pg respectively. Stipa purpurea, Carex moorcroftii, and Stipa purpurea-Kobresia pygmaea- communities contributed 69.3% to the total biomass of alpine grassland due to their large coverage and high biomass carbon density. (2) The average biomass carbon density was 690.80 g C·m^-2 in alpine grassland. S. purpurea(196.14 g C·m^-2) andRosa multiflora(177.93 g C·m^-2) had the highest aboveground biomass carbon density (AGC), while R. multiflora (1491.18 g C·m^-2) andS. purpurea-K. pygmaea (1306.51 g C·m^-2) had the highest belowground biomass carbon (BGC), which were significantly higher than other communities (P<0.05). (3) The vertical distribution of BGC could be divided into two types. Communities of Ceratoides latens,Kalidium foliatum, Potentilla fruticosa, S. purpurea, Carex moorcroftii,S. purpurea-K. pygmaea, R. multiflora, Orinus thoroldii and Sophora moorcroftiana were classified as the “exponential function type”, with BGC of which being mainly distributed in the 0-10 cm soil depth. Blysmus sinocompressus community was classified as the “quadratic function type”, with BGC of which being mainly distributed in the depth of 40-60 cm. Evaluation of above and below ground biomass carbon storage of different grassland communities is meaningful for improving the accuracy of biomass carbon estimation, providing data support for grassland management.

Differences in leaf litter decomposition and its temperature sensitivity among woody species with different mycorrhizal associations in a peatland in the Daxing’an Mountain.

LIU Shan-shan, SHI Fu-xi, XU Jia-wen, WU Pan-pan, MAO Rong

2020, 39(5):  1417-1725. 

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Using leaf litters of three ectomycorrhizal woody species (Salix rosmarinifolia, Betula platyphylla, and B. fruticosa) and four ericoid mycorrhizal woody species (Vaccinium uliginosum, Ledum palustre, Chamaedaphne calyculata, and Rhododendron parrifolum) from a permafrost peatland in the Daxing’an Mountain of China, we compared the differences in carbon (C) mineralization and mass loss during litter decomposition at  10 and 20 ℃, and temperature sensitivity of C mineralization and mass loss between ectomycorrhizal and ericoid mycorrhizal woody species in a 315day laboratory incubation experiment. We found that ectomycorrhizal species had greater C mineralization and mass loss than ericoid mycorrhizal species during litter decomposition at both 10 and 20 ℃. Compared with ericoid mycorrhizal species, litters of ectomycorrhizal species had higher temperature sensitivity of C mineralization, but lower temperature sensitivity of mass loss. In addition, C mineralization and mass loss correlated positively with litter nitrogen (N) and phosphorus (P) concentrations, but negatively with C∶N and C∶P ratios. Temperature sensitivity of mass loss correlated negatively with litter N and P concentrations, but positively with C∶N and C∶P ratios. However, there was no significant relationship between temperature sensitivity of C mineralization and litter initial chemical properties. Our results  will help understand and predict the effects of climate warming and associated shifts in species composition on litter decomposition in boreal peatlands.

Dynamics of potassium (K) and sodium (Na) return in litterfall in a Larix mastersiana-Abies faxoniana primary forest.

ZENG Xin, FU Chang-kun, YANG Jia-ping, ZHU Liang, WU Fu-zhong, ZHANG Li

2020, 39(5):  1426-1435. 

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Nutrient return with litters is the main process of ecosystem material cycling and an important source of nutrients for tree growth. Compared with other elements, potassium (K) and sodium (Na) play an extremely important role in regulating osmotic pressure. Both elements are easy to be lost, as their leaching is strong. However, there is a lack of necessary attentions. We investigated the return characteristics of K and Na in different types of litter from September 2015 to August 2016 in a primary dark coniferous forest (3589 m a.s.l.), which was dominated by Larix mastersiana andAbies faxoniana. The results showed that: (1) The amount of annual return of K and Na in litter was 25.34 and 4.44 kg·hm^-2, respectively, with the order of different organs: foliar litter>twig litter>miscellaneous>bark litter>epiphytic litter>reproductive organ litter. Among them, foliar litter and twig litter accounted for more than 85% of the total return of K and Na. (2) The return dynamics of K and Na in total litter, foliar litter and twig litter presented “bimodal”patterns, with the maximum values in May and October. The dynamics of K and Na returns in bark litter and reproductive organ litter showed a “unimodal” pattern, with a maximum in May. (3) The K and Na in tree litters showed a “bimodal” return pattern, with the maximum values in May and October. The K and Na returns in shrub litters showed a “unimodal” pattern, with peaks in September to October. These results illustrate the seasonal characteristics of element return in different types of litters in typical coniferous forests in alpine areas, providing basic reference for further understanding regional forest material cycling and related ecological processes.

Effects of soil warming on water extractable organic carbon in subtropical forest.

BAI Hao-yu, YANG Zhi-jie, ZHENG Yong, XIONG De-cheng, ZHOU Jia-cong

2020, 39(5):  1436-1444. 

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Water extractable organic carbon (WEOC) is sensitive to climate change, and thus plays a vital role in carbon cycling in forest ecosystems. Here, the effects of soil warming (+5 ℃) on soil WEOC extracted by three different methods were examined in a subtropical forest. Concentrations of WEOC extracted by cold water (C_WEOC) and salt solution (S_WEOC) were not affected by soil warming. Soil warming reduced the concentration of WEOC extracted by hot water (H_WEOC) by 51.2% at the 0-10 cm soil layer, but elevated H_WEOC by 67.1%, 781.7%, and 501.6%, respectively, at the 10-20, 20-40 and 40-60 cm soil layer. Soil warming increased microbial biomass carbon (MBC) by 98.2% and 163.1% at the 20-40 and 40-60 cm soil later, respectively, but had no effect on MBC at the 0-10 and 10-20 cm. There was a significant difference in soil WEOC concentrations extracted by the three different methods. Generally, the concentration of C_WEOC was the lowest among the three extraction methods, and H_WEOC and S_WEOC were the highest in surface soil layer and deep layer, respectively. The significant effect of soil warming on WEOC could be ascribed to warmingstimulated deeper rooting, which enhance root carbon input and microbial activity in the subsoil and thus induce a decrease of WEOC in the topsoil and an increase of WEOC in the subsoil. Different extraction methods could be used together to reflect different origins and transformations of WEOC. These results could facilitate our understanding of the responses of soil carbon cycling to climate change in subtropical forests.

Dynamics of soil physicochemical properties and microbial biomass in a Pinus sylvestris var.mongolica plantation.

LIN Ya-chao, GAO Guang-lei, DING Guo-dong, WANG Xue-lin, WEI Xiao-shuai, WANG Long

2020, 39(5):  1445-1454. 

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To reveal the dynamics of soil physicochemical properties and microbial biomass as well as their relationships in Mongolian pine (Pinus sylvestris var.mongolica) plantations with different stand ages, we examined soil physicochemical properties and soil microbial biomass C (MBC) and N (MBN) in Mongolian pine plantations of various ages in Mu Us, Horqin, and Hulunbuir sandy lands. The results showed that changes of soil physicochemical properties with increasing stand age differed among different sandy lands. In the Mu Us Sandy Land, soil bulk density and soil nutrients significantly decreased. In the Horqin Sandy Land, soil porosity and nutrients significantly increased. In the Hulunbuir Sandy Land, soil nutrients increased first and then decreased. With increasing stand age, soil MBN decreased in the Mu Us Sandy Land, increased in the Horqin Sandy Land, and increased first and then decreased in the Hulunbuir Sandy Land. The major factors affecting soil MBN were the concentrations of nitrate, ammonium, and organic matter in the Mu Us, Horqin, and Hulunbuir Sandy Land, respectively. Soil nitrogen was the main limiting factor of Mongolian pine plantation in the Mu Us and Horqin Sandy Land, while soil organic carbon was the main limiting factor in the Hulunbuir Sandy Land.

Effects of forest secondary succession and soil depth on microbial community structure.

SHAO Peng-shuai, XIE Hong-tu, BAO Xue-lian, LIANG Chao

2020, 39(5):  1455-1463. 

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Forest secondary succession closely relates with the dynamics of ecosystem structure and function. Previous studies have reported the changes of plant community and soil organic carbon (SOC) during forest succession, with limited understanding of the responses of soil microbial community. Here, we explored the changes of soil microbial community structure (represented by phospholipid fatty acid) across secondary forest succession (20, 80, 120, 200, and ≥300 years) and soil depth (topsoil and subsoil). We demonstrated that the changes in microbial community structure among forest successional stages were ascribed to the specific microbial functional groups. Soil microbial community was dominated by Gram-negative bacteria and saprotrophic fungi at earlysuccessional stages, and by Gram-positive bacteria and arbuscular mycorrhizal fungi at late-successional stages. Quantity and quality of soil organic matter (SOM) were the predominant factors driving soil microbial community structure and biomass. The increase in SOC contents at early and middle successional stages stimulated microbial biomass, and the increase in soil aromatic compounds suppressed microbial biomass at late-successional stages. Soil microbial community was affected by the varied soil physicochemical properties between topsoil and subsoil, e.g., high SOC content in topsoil correlated with microbial biomass. Our findings suggest that changed soil microbial community and its driving factors in temporal and spatial scales reflect the response of ecosystem structure and function to environmental change.

Greenhouse gas emission of wetland soils and its influencing factors in permafrost degradation area.

XU Li, LI Cheng-xu, ZHANG Jun-hui, FENG Yue, ZHANG Lei, HAN Shi-jie

2020, 39(5):  1464-1473. 

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We measured the emission fluxes of greenhouse gases (CH₄, CO₂, and N₂O) during the growing season from wetland soils of differently degrading permafrost (seasonally frozen soil, perennially discontinuously frozen soil and continuous permafrost, represented by D1, D2 and D3, respectively) around Xing’an Mountains by insitu static chambergas chromatography method. The effects of environmental factors on greenhouse gas emission were analyzed. The results showed that: (1) During the growing season, the wetland soils of all the three frozensoil regions were sources of CO₂ and N₂O, the soils in D1 and D3 were the sources of CH₄, while soil in D2 was CH₄ sink. The average fluxes of CH₄ during the growing season in the three frozen soils were (0.127±0.021), (-0.020±0.006) and (0.082±0.019) mg·m^-2·h^-1, respectively. The average CO₂ fluxes were (371.50±66.73), (318.43±55.67) and (213.19±37.05) mg·m^-2·h^-1, respectively. The average N₂O fluxes were (24.05±2.62), (8.07±2.42) and (2.17±0.25) μg·m^-2·h^-1, respectively. The emissi〖HJ*3〗on fluxes of CO₂ and N₂O increased with the degradation of permafrost. (2) Fine root biomass, litter biomass, total carbon content, total nitrogen content, dissolved organic carbon content, total dissolved nitrogen content, soil bulk density, soil temperature and soil moisture were the factors driving greenhouse gas emission. Variations in emission fluxes of CH₄, CO₂ and N₂O were the results of the interactions among different factors in the three frozen soil regions.

Effects of different CO₂ concentrations and nitrogen application levels on content and accumulation of non-structural carbohydrate in stem sheath of Japonica rice.

CAO Pei-ei, YANG Kai, LYU Chun-ua, HUANG Yao, YU Ling-fei, HU Zheng-hua, SUN Wen-juan

2020, 39(5):  1474-1483. 

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To investigate the effects of elevated CO₂ concentration \[CO₂\] and nitrogen fertilization on the content and accumulation of non-structural carbohydrate (NSC) in stem sheath of rice, a Japonica rice (Oryza sativa L.) ‘Nanjing 9108’ was grown in a OTC pot experiment with three CO₂ concentrations: ambient (T0), ambient+120 μmol·mol^-1 (T1), and amibent+200 μmol·mol^-1 (T2) in opentop chambers (OTC), and three nitrogen (N) fertilization levels: 10 g N·m^-2 (N1), 20 g N·m^-2 (N2), and 30 g N·m^-2 (N3). We measured aboveground biomass, NSC content in stem sheath and nitrogen content in the top four leaves at heading, filling (20 d after heading), and mature stage. Results showed that there was no significant effect of elevated \[CO₂\] on N content in leaves at the heading stage, while it significantly reduced the N content in leaves at N2 and N3 levels during the filling stage. Elevated \[CO₂\] did not affect the content and accumulation of NSC in stem sheath at the heading stage. The accumulation of NSC in stem sheath significantly increased when the pots were transferred to higher \[CO₂\] at the heading stage, but significantly decreased when the pots were transferred to lower \[CO₂\] at the heading stage. Under the same \[CO₂\], both the content and accumulation of NSC were N1>N2>N3, being significantly higher under N1 than under N3. There was no significant difference in rice yield at different \[CO₂\], but the yield increased with the increasing N fertilization levels. Elevated \[CO₂\] and N fertilization levels significantly interacted to affect the content of NSC in stem sheath during the filling period. The content and accumulation of NSC in stem sheath at the heading and filling stages were positively correlated with dry weight of stem sheath and negatively correlated with N content in leaves. The slower N attenuation in leaves, the lower NSC residual ratio (R_NSC) was. There was a significant negative correlation between seed setting rate, yield and R_NSC at the filling stage, suggesting that there would be less NSC transferred out from stem sheath, lower seed setting rate and lower yield with higher R_NSC.

Effects of flooding and salt stress on the growth of Zizania latifolia.

CHEN Fang-yuan, GU Yong-bo, BAI Jiang-shan, LOU Yan-jing

2020, 39(5):  1484-1491. 

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In Songnen Plain of northern China, salt marsh has been threatened by increasing flooding and soil salinity-alkalinity since the late 20th century. To explore how plants respond to such environmental changes, we examined the effect of flooding stress and saline stress on growth of Zizania latifolia under greenhouse conditions. We conducted a pot experiment with four water depths (5, 15, 30, and 60 cm) and four salinity levels (0, 15, 50, and 100 mmol·L^-1) and explored the tolerance and adaptive strategies of Z. latifolia, aiming to provide a reference for the protection and restoration of saline-alkali wetlands in this region. The results showed that: (1) Flooding had a significant effect on the growth and biomass allocation of Z. latifolia(P<0.05). As the water depth increased, plant height and aboveground biomass increased, while rhizome length, root length, total biomass, underground biomass and root-shoot ratio significantlydecreased. Leaf area showed a downward trend after a rise. (2) Salinity had significant effects on all the examined traits except root-shoot ratio. Plant height, leaf area, rhizome length, root length, total biomass, aboveground and underground biomass of Z. latifolia significantly decreased with increasing salinity (P<0.05). (3) Water depth and salinity significantly interacted in their effects on plant height, aboveground and underground biomass (P<0.05). In general, Z. latifolia survived in 60 cm water depth and 100 mmol·L^-1 salinity. However, the growth of Z. latifolia varied among different stress conditions. We concluded that Z. latifolia is highly tolerant to flooding and can resist flooding stress through elongating shoot and allocating more biomass to aboveground, while it shows poor tolerance to salt stress, which has negative effects on its morphological development and biomass accumulation.

Distribution patterns and influencing factors of naturalized plant species in Heilongjiang, Jilin, Liaoning, and Inner Mongolia.

2020, 39(5):  1492-1500. 

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Based on field investigation and data collection, we estimated the distribution pattern and driving factors of naturalized plant species in 48 prefecturelevel cities in four provinces (Heilongjiang, Jilin, Liaoning and Inner Mongolia) of Northeast China. We found 370 species from 239 genera and 70 families of naturalized plant species in this area. Among those species, Asteraceae, Poaceae and Fabaceae had the largest proportion of species. About 70% of the naturalized species were introduced artificially, with Europe as the largest source area. There was substantial spatial variability in species diversity, with a decreasing trend from east to west in prefecturelevel cities. Naturalized 〖HJ*5〗species distributed more in capital cities or coastal cities, such as Shenyang, Harbin, Hohhot and Dalian, while less distributed in plains and grasslands. GDP, land use intensity and mean annual temperature were major driving factors. By Logistic fitting, we found that the number of naturalized species in our study region tended to be stable. However, more exotic plant species may be introduced in the future with the implementation of “Northeast Revitalization” policy, which should be paid more attention.

Spatial and temporal dynamics of phytoplankton community structure in Haizhu National Wetland Park.

ZHU Ming-ming, FAN Cun-xiang, WU Zhong-kui, QIU Xiao-chang, HUANG Ye-hui, RONG Yu-qin1, ZHAO Jian-gang, ZHONG Wen, ZHANG Xiu-feng

2020, 39(5):  1501-1508. 

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Phytoplankton is an important component of wetland ecosystems. Changes in the quantity and community structure of phytoplankton may affect the structure and function of wetlands.  The spatial and temporal dynamics of phytoplankton in Haizhu National Wetland Park in winter (2017) and summer (2018) were investigated. Results showed that 171 species belonging to 64 genera in seven phyla were recorded. Chlorophyta, Bacillariophyta and Cyanophyta accounted for 44%, 26% and 13% of all the species, respectively. The dominant species wereMerismopedia cantonensis and Merismopedia minimain both seasons, with Cryptomonas erosa being also among the dominant species in winter. The community structure, cell density and biodiversity index of phytoplankton varied significantly between seasons. In winter, the community was dominated by bacillariophyta and chlorophyta, accounting for 32% and 29% of the phytoplankton; whereas in summer, the community was dominated by cyanophyta, with a 68% contribution. The abundance of phytoplankton in summer was (25.58±18.47) ×10⁶ cells·L^-1, about three times high as that in winter. The Shannon index and Pielou index showed similar trends, being high in winter (4.38 and 0.77) and low in summer (2.92 and 0.51). Spatially, species richness and diversity index were low, but abundance was high in Haizhu Lake. The abundance of bacillariophyta was the highest in the wetland of Tang River and Xijiang River, while other sites were dominated by cyanobacteria. Total nitrogen and temperature were important factors affecting the phytoplankton community structure. Our results are useful for management and protection of Haizhu National Wetland Park.

Flora, structure, and dynamics of Davidia involucrata community in Daxiangling Nature Reserve.

ZHANG Xiao-yue, ZHOU Run-hui, YU Fei-yan, YE Xin, WANG Min, QI Jin-qiu, HAO Jian-feng

2020, 39(5):  1509-1517. 

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Based on data from several investigations, we explored flora composition, structure, regeneration status and succession of Davidia involucrata community in Daxiangling Nature Reserve, Sichuan. The results showed that: (1) The vegetation was a transition flora type from subtropical to temperate zone. The coexistence of many ancient genera reflected the ancient and solitary of flora. (2) The diameter-class structure of the community was biased with a normal distribution, and the height-class structure showed an inverted J-shaped curve. The development trend of community structure was relatively stable. (3) The age structure of D. involucratapopulation was approximately pyramidal, as a growing type. Overall, the pure D. involucrata forest (community type C) was the best in matching dominance and at the late stable succession stage, which was the climax community in Daxiangling Nature Reserve. Our results suggested that establishing a special protection area for in situ conservation of D. involucrata is an effective method for the conservation of native communities.

Trade-off among leaf traits of typical greening tree species in Lanzhou.

YANG Ke-tong, CHEN Guo-peng, LI Guang, YU Xiao-ya, ZHANG Kai, TANG Dong, ZHANG Wen-xiang, GUO Ying-jie

2020, 39(5):  1518-1526. 

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The trade-off relationship among plant leaf traits reflects the high adaptability of plants and their self-regulation ability in complex habitats. Understanding the trade-offs among leaf traits of urban greening tree species in sem-arid regions, and comparing the allometric growth of tree species with different growthforms (coniferous and broadleaved) would help to further understand the evolutionary of plants. Here, we measured leaf traits of 13 coniferous tree species and 47 broadleaved tree species, which are typical greening tree species in Lanzhou. We compared the trade-off relationships among leaf traits by the standardized major axis estimation (SMA) and phylogenetically independent contrast analysis (PIC). The results showed that the relationship between leaf area, leaf volume and leaf dry weight of different life-form tree species was isometric, with no significant difference between coniferous and broad-leaved tree species. A weak trade-off relationship was found between leaf thickness and leaf area. The allometric coefficient between leaf length and leaf width of broad-leaved species was 0.764. The trade-off among leaf traits of typical greening tree species in Lanzhou suggested long-term adaptation of those species to the habitat of Loess Plateau and a covariant relationship among some traits. The trade-offs in broad-leaved tree species indicated that those species showed the characteristics of rapid investment-return.

Differences of forage quality between Fargesia denudataand F. robusta.

ZHANG Quan-jian, LAI Chang-hong, GONG Xu, ZHANG Yuan-bin

2020, 39(5):  1527-1537. 

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Fargesia denudata in Min Mountains and F. robusta in Qionglai Mountains are forage species with the highest foraging frequency by wild giant panda. Taking F. denudatain Wanglang Nature Reserve andF. robusta in Wolong Nature Reserve as the study objects, we compared their forage quality through measuring nutritional components, tannins and total phenols content, inorder to provide reference for the establishment of future potential habitat, corridor and pure plantation with favorable bamboo species for wild giant panda. The results were as follows: (1) F. denudata was superior to F. robusta in terms of crude protein and crude fiber concentrations (P<0.05). (2) F. denudatawas inferior toF. robusta in the contents of calcium in shoots and stems, and phosphorus in shoots and leaves (P<0.05). (3) For concentrations of tannins, total phenols, and total amino acids, the leaves ofF. robusta were more superior (P<0.05), whereas shoots and stems of F. denudata were more superior in terms of tannins, and its shoots in terms of total phenols and stems in terms of total amino acids were more superior (P<0.05). (4) With regard to crude fat, although the stems of F. denudata and the shoots and leaves of F. robusta were slightly superior to the counterparts, but the differences were not statistically significant (P>0.05). We concluded that both species had advantages and disadvantages in forage quality with respect to nutritional components, tannins and total phenols. If used together, they would be complementary in intake of crude protein, total amino acids, calcium and phosphorus, and can diminish the intake of tannins and total phenols. As those two bamboo species are preferred forage species of giant panda, mixture of both could be planted in the potential habitats, corridors, and pure plantation forest establishments in the related areas of the Min Mountains and Qionglai Mountains.

Growth, physiological and biochemical response of Baccaurea ramifloraLour. seedlings to different shading environments.

HUANG He-teng, HUANG Jian-jian, CHEN Jie, CHEN Yu-juan, GUAN Dong-sheng

2020, 39(5):  1538-1547. 

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Baccaurea ramifloraLour. is a native tropical tree species with different light adaptability at seedling stage and maturity stage. Clarifying the growth, physiological and biochemical response mechanisms of B. ramiflora seedlings to different shading environments can help determine the suitable light environment for seedling growth, which is of great significance for cultivation and ecological application. Five shading treatments were set up, including CK (natural light), S3 (shading rate of 45.3%), S4 (shading rate of 69.2%), S6 (shading rate of 80.0%) and S8 (shading rate of 90.2%). Growth and physiological changes of seedlings from Tingkou Mountain and Xiexie Mountain were measured after four months of treatment. With the increases in shading, leaf area and photosynthetic pigment content of B. ramiflora seedlings increased, while chlorophyll a/b value and catalase (CAT) activity decreased. Malondialdehyde content decreased firstly when shading rate was ≤S6, and then slightly increased in S8. Plant height and ground diameter firstly increased and then decreased, while electrical conductivity, proline (Pro) and soluble sugar (Ss) contents firstly decreased and then increased. Under strong light conditions, B. ramiflora seedlings eliminated membrane lipid peroxidation by increasing CAT activity and the relative content of carotenoids. Under low light conditions, seedlings increased light energy utilization by enhancing leaf area and photosynthetic pigment content. Pro and Ss, as comprehensive regulatory substances, could alleviate cell membrane stress caused by strong light and weak light by changing osmotic pressure. Pro and Ss contents of seedlings from Tingkou Mountain and Xiexie Mountain were the lowest under the treatments of S6 and S4, respectively, while the increase of plant height and ground diameter was the highest under the treatments of S6 and S4, respectively. Our results indicated that B. ramiflora at seedling stage exhibited the characteristics of shading plants. In other words, strong light or heavy shading will inhibit its growth. The seedlings from Tingkou Mountain were more shade-tolerant than that from Xiexie Mountain, highlighting the effects of long-term differences of light environment in their provenances.

Coupling effects of regional temperature and precipitation on radial growth of Larix principis-rupprechtii at different altitudes in Guandishan.

REN Xu-ming, GONG Yuan-qi, WANG Ping-an, BO Fu-jing, ZHANG Yun-xiang, GUO Jin-ping

2020, 39(5):  1548-1557. 

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To reveal the coupling effects of regional temperature and precipitation on the radial growth of trees in mountainous forests at different elevations, we collected tree cores of typical sample woods from Larix principis-rupprechtiiplantations with similar conditions across four elevations in the Xiaowen Forest Farm of Guandishan forest region and the Pangquangou National Nature Reserve. We established chronology to obtain the annual ring width index and conducted correlation analysis and singleyear analysis combined with regional temperature and precipitation. The results showed that radial growth ofLarix principis-rupprechtii was closely related to regional temperature and precipitation on the four elevations, but with different response mechanisms. At the altitude of 1600 m, annual ring width index was significantly negatively correlated with temperature in April, and positively correlated with precipitation in September. At 1800 m, annual ring width index was significantly negatively correlated with temperature and positively correlated with precipitation in June of last year. At 2000 m, annual ring width index was significantly negatively correlated with temperature in September and precipitation in March. At 2200 m, annual ring width index was significantly positively correlated with temperature and negatively correlated with precipitation in August of last year. With increasing altitude, the temperature decreased and precipitation increased. Moreover, the coupling effect of temperature and precipitation on the radial growth ofLarix principis-rupprechtii was changing. When the altitude reached 2000 m, the increase in precipitation in the growing season altered the coupling effects.

Effects of pig slurry application on phosphorus utilization and stoichiometry of nitrogen and phosphorus in direct seeding rice.

TIAN Huai-feng, MA Jun, YE Ying, ZHAO Kao-cheng, GAO Wei, HUANG Li-fen, ZHUANG Heng-yang

2020, 39(5):  1558-1565. 

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A field experiment with different amounts of pig slurry as base fertilizer and panicle fertilizer was carried out in  Shanghai Farm to examine the impacts of pig slurry application on phosphorus absorption and utilization and the ecological stoichiometry of nitrogen and phosphorus in direct seeding rice. The results showed that pig slurry application had significant effects on dry matter accumulation and concentrations of nitrogen and phosphorus in direct seeding rice. The dry matter accumulation and yield of rice increased with the amount of pig slurry application. Phosphorus concentrations in the rice plants at jointing, heading, and mature stages and in straw and grain were significantly positively correlated with the amount of pig slurry application. During the growing season, plant N∶P ratios under different treatments ranged from 3.13 to 5.10, with the ranges of 3.13-4.83, 3.42-4.35 and 3.98-5.10 at jointing, heading and maturity stages respectively, being lower at the heading stage. Straw N∶P ratios showed greater variation, with a range of 4.30-6.57. The variation of N∶P ratios in grain was smaller, with a range of 3.85-4.37. Plant N∶P ratios at the heading and maturity stages, and that of straw and grain were significantly positively correlated with the total amount of pig slurry application, indicating that pig slurry application had a more considerable effect on nitrogen uptake than phosphorus uptake of direct seeding rice.

Effects of straw returning on activities and gene expression of key enzymes related to tuber starch synthesis in rainfed potato.

SU Wang, XIE Rui-rui, WANG Jian

2020, 39(5):  1566-1574. 

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A field experiment was conducted to investigate the effects of straw returning on activities and gene expression of key enzymes related to tuber starch synthesis in rainfed potato (Qingshu 9) during tuber formation. We measured the activities and gene expression of key enzymes related to starch synthesis, starch gelatinization characteristics, and starch accumulation. Theresults showed that straw returning significantly enhanced activity of SSS enzyme, gene expression of SSII and SSIII, starch breakdown, amylase content and ratio of amylase to amylopectin, and decreased activities of AGPP and GBSS enzyme, gene expression of AGPase, GBSSI, SBEI, and SBEII, starch viscosity at various stages, starch retrogradation, and total starch content, but not affected SBE enzyme activity and starch pasting temperature in the whole process of tuber formation. GBSS enzyme activity was significanly positively correlated with AGPase, SBEIgene expression, and negatively correlated with amylase content and ratio of amylase to amylopectin. SBE enzyme activity was significantly positively correlated with SSIIgene expression, peak viscosity, trough viscosity, final viscosity and total starch content, and negatively correlated with starch breakdown and pasting temperature. AGPase gene expression was significantly negatively correlated with amylase content.GBSSIgene expression had a significantly positive correlation with starch final viscosity and starch retrogradation, and a significantly negative correlation with starch pasting temperature. Starch gelatinization was not significantly correlated with starch accumulation.

Dynamics of soil dissolved organic carbon and inorganic nitrogen during remediation of degraded facility vegetable soil.

JI Chun-yang, FENG Jing-xian, HE Yun-hua, SUN Xiao-fei, LI Shou-zhong, YIN Yun-feng

2020, 39(5):  1575-1582. 

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Reductive soil disinfestation (RSD) is an effective method to restore degraded facility vegetable soil. However, RSD may cause the leaching of dissolved organic carbon (DOC) and inorganic nitrogen (NO₃^--N and NH₄⁺-N). In this study, we used rice straw and biochar (BC) as remediation materials to investigate the dynamics of soil basic properties, the contents of DOC and inorganic nitrogen during the remediation process in an experiment with BC, RSD and RSD+BC treatments. Compared with control, BC treatment significantly increased soil pH, EC and DOC content (P<0.05), and did not affect soil NO₃^--N and NH₄⁺-N contents. Soil NO₃^--N content decreased rapidly in RSD and RSD+BC treatments within 1-3 days, and then maintained at a low level. Furthermore, the contents of DOC in the RSD and RSD+BC treatments increased firstly and then decreased, and were significantly higher than those in the control during the whole incubation period (P<0.05). BC and RSD significantly interacted to affect soil DOC, TC, TN and C/N. In summary, RSD and RSD+BC treatments can effectively remove NO₃^--N, but with a risk of leaching due to the increases of DOC.

Comparison on life history traits of two Moina species from shallow lakes in subtropical China.

ZHANG Fei-yun, WANG Zi-yan, LI Jun, CAO Ya-qin, QI Hui-ying, SUN Yu-chen, ZHANG Ting-ting, DENG Dao-gui

2020, 39(5):  1583-1589. 

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The life history parameters (e.g. body length, time to maturation, survival rate, lifespan and the number of offspring) of Moina weismanni from Lake Nanhu in Wuhan (Hubei Province)and Moina micrura from Lake Taihu in Jiangsu Province were examined under 2×10⁵cells·mL^-1Scenedesmus obliquus at (25±1) ℃. The results showed that body length of bothMoina species showed an increasing trend with increasing instar number. Time to maturation （P=0.008) and the first reproduction time (P=0.022) of M.weismanni were significantly lower than those of M. micrura, whereas body length at maturity (P<0.001), lifespan (P=0.003) and the number of offsprings at first reproduction (P<0.001) of M.weismanni were significantly higher than those of M. micrura. Innate rate of increase was 0.73 ind·d^-1 forM. weismanni and 0.49 ind·d^-1 for M. micrura. Results from Pearson correlation analysis showed that there were significant relationships between the number of offspring at first reproduction and body length at maturity for both M.weismanni(r=0.659,P=0.008) and M. micrura (r=0.649, P=0.009). Our results suggested that M. micrura from Lake Taihu had a longer time to maturation, whereas M. weismanni from Lake Nanhu had a stronger reproductive ability, which might be related to differences in their genetic structure and adaptation to environmental factors in two lakes.

Integration of natural reserves based on potential habitat protection of the Amur tiger.

GU Yuan-yang, ZHANG Fang-ling, LIANG Xiao-yu, LIU Chang, XING Shao-hua, WANG Qing-chun

2020, 39(5):  1590-1599. 

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Amur tiger is classified as the first-class protected wild animal in China. They live predominantly in several nature reserves in Zhangguangcailing, Laoyeling, and Wandashan. A large number of different types of protected areas, such as forest parks, scenic spots and wetland parks, are distributed around those nature reserves. Those protected areas can provide habitats for Amur tigers to a certain extent. However, issues related to management objectives, management mechanisms and other anthropogenic factors resulted in habitat isolation, spatial overlap and other chaotic phenomena. To facilitate the establishment of a natural reserve system with national parks as the main body to carry out comprehensive protection, and to provide support for the construction of the Northeast China Tiger and Leopard National Park, we used MaxEnt model to predict Amur tigers’ potential habitats based on 44 Amur tiger distribution points and 11 related environmental variables. Based on the distribution pattern of suitability levels of the national naturereserves, national forest parks, national wetland parks and the habitat of Amur tiger, a cost distance method was used to integrate the natural protected areas within the habitats for Amur tiger. The results showed that: (1) The potentially suitable habitats for Amur tigers in China were mainly concentrated in Muling City, Hunchun City, Dunhua City, Ning’an City, Yanji City, Hailin City, Dongning County, Wangqing County, Raohe County, and Baoqing County, with a total area of about 10000 km², accounting for 1.5% of the total area of Heilongjiang and Jilin provinces. (2) The potential distribution range of Amur tigers are about 51000 km², accounting for 8% of the total area of those two provinces. (3) With the contour value of 0.5 in the cost distance diagram as the boundary, 30 nature reserves and 47 surrounding protected areas were divided into nine protectedarea groups, with a total area of 77818.7 km². Our results will provide reference for the conservation of Amur tiger and the integration of the associated protected areas in the future.

Pigmentation change on beak for Sthenoteuthis oualaniensis in the Xisha Islands waters of the South China Sea.

LU Hua-jie, CHEN Zi-yue, NING Xin, CHEN Xin-jun

2020, 39(5):  1600-1608. 

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Beak is the feeding organ of cephalopods, which could provide abundant information on cephalopod fishery biology and ecology. We measured beak pigmentation in 860 purple-back flying squid (Sthenoteuthis oualaniensis) samples collected by Chinese lighting falling-net vessels in the Xisha Islands waters of the South China Sea from May to August 2017. We analyzed the relationship of changes in beak pigmentation with mantle length (ML), body weight (BW), somatic body weight (SBW), sexual maturity, and the external morphological parameters of the beak. The results showed that there were significant sexual variations in the beak pigmentation of S. oualaniensis (P<0.05), with higher pigment rates in females. The relationships between the pigmentation and ML, BW and SBW were positive. Pigmentation increased with the increasing sexual maturity stage. The velocity of male pigmentation in the lower beak was faster than the upper beak, except the lower wing length. However, the velocity of female pigmentation in the lower beak was slower than that in the upper beak. Our results provide a basis for the fishery biology research and for effective exploitation and scientific management of S. oualaniensis resource.

Effects of seawater acidification and warming on growth and pigmentation in juvenile sea cucumber Apostichopus japonicus.

SONG Ming-shan, YANG Xiao-long, ZHANG An-guo, LIU Yong-jian, YANG Da-zuo, ZHAO Huan, YUAN Xiu-tang

2020, 39(5):  1609-1616. 

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Ocean acidification and warming are the main environmental pressures and ecological problems faced by marine organisms and their dependent ecosystems at present and in the future. However, the research on the early development of marine organisms mainly focused on the impact of ocean acidification. To better understand the impacts of climate change on marine organisms, it is necessary to study the responses of marine organisms under the joint effect of ocean acidification and warming. We conducted an experiment with juvenile sea cucumber (Apostichopus japonicus) to examine the impacts of seawater acidification and warming on growth, development, and body pigmentation in key stage of body pigmentation by simulating current seawater condition and that at the end of this century. Four treatments were set up: control group (seawater temperature of the Dalian coast, pCO₂ 400 mg·kg^-1), seawater warming group (control group temperature plus 2 ℃, pCO₂ 400 mg·kg^-1), seawater acidification group (control group temperature, pCO₂ 1000 mg·kg^-1), and combined seawater warming and acidification group (control group temperature plus 2 ℃,pCO₂ 1000 mg·kg^-1). The results showed that a pH decrease of 0.23 units delayed growth, slowed pigmentation, and increased variation of body weight among individuals. In contrast, a 2 ℃ temperature increase accelerated growth and pigmentation of the juveniles, potentially neutralizing the negative effects of pH decrease. Our results indicated that juvenile sea cucumbers can gradually adapt to long-term seawater acidification and warming.

Community structure of benthic macro-invertebrates and biological assessment of water quality in the inflowing rivers of Lake Gehu in spring.

SHAO Yong, WANG Hong-yang, XU Jiao, HANG Dan, LU Yong-jun, LU Yan, WU Pan, ZHU Ming-cheng

2020, 39(5):  1617-1628. 

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In this study, we investigated the community structure of benthic macro-invertebrates in the inflowing rivers of Lake Gehu in April of both 2018 and 2019, and evaluated water quality using biological indices. Twenty-eight species of benthic macro-invertebrates were identified in the inflowing rivers of Lake Gehu. Limnodrilus hoffmeisteri (dominance index: 0.46) with high pollution resistance and Bellamya aeruginosa (dominance index: 0.11) with moderate pollution resistance were the dominant species. In terms of biodiversity, Hexi River was the highest, followed by Huangli and Biandan rivers; Xiaxi River and the estuary into the lake were the lowest. The distribution of aquatic plants might be one of the most important factors determining the diversity of benthic macroinvertebrates in different regions. The Carlson nutrition status index was consistent with the biological indices in water quality assessment. With the extension of Xinmeng River and dredging project, the middle and upper reaches of Hexi, Xiaxi, and Huangli rivers were at a moderate eutrophication level, with water body being lightly to moderately polluted; whereas the lower reaches of Biandan River and estuaries into the lake were at a severe eutrophication level, with water body being moderately to heavily polluted.

Comparison of swimming ability among five freshwater fish species.

FU Xiang, FU Cheng, FU Shi-jian

2020, 39(5):  1629-1635. 

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To investigate the physiological mechanism underlying the maximum aerobic and anaerobic swimming ability and preferred swimming speed of fish in different habitats, we measured the critical swimming speed (U_crit), maximum constant accelerated swimming speed (U_cat), preferred swimming speed (U_pref), standard metabolic rate (SMR), maximum metabolic rate (MMR), and aerobic metabolic scope (MS) of the juvenile fish of five species at （25±1） ℃, including Spinibarbus sinensis, Carassius auratus gibelio, Procypris rabaudi, Mylopharyngodon piceusand Myxocryprinus asiaticus. Results showed that Spinibarbus sinensis showed the strongest swimming ability (both aerobic and anaerobic). Mylopharyngodon piceus and Myxocryprinus asiaticus were poor swimmers. The U_pref of all the five species fell into the range from 10 to 24.5 cm·s^-1, despite their significant variation in swimming ability. These results suggested that swimming ability of the selected fish species were mainly determined by cardiorespiratory capacity and morphology-induced swimming efficiency. Our results have certain reference value for designing fishways.

Remote sensing-based identification of forest types and the scale effect in subtropical evergreen forests.

ZHANG Yue-nan, FANG Lei, QIAO Ze-yu, CHEN Long-chi, ZHANG Wei-dong, ZHENG Xiao, JIANG Tao

2020, 39(5):  1636-1650. 

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Optical remote sensing (ORS) is the primary tool to obtain information on regionalscale vegetation cover. Few efforts have been made to identify forest types within subtropical evergreen forests using ORS. Scale effects have been reported in literature, yet the optimal spatial resolution to identify evergreen forest types is still unclear in practical application. In this study, we used four types of ORS imagery \[Pléiades (2 m), RapidEye (5 m), and Landsat-8 (15 m and 30 m)\] to investigate whether the classification of three typical evergreen forest types \[Chinese fir forest (CFF), Masson pine forest (MPF), and evergreen broadleaved forest (EBF)\] in subtropical landscapes would be influenced by scale effects. Moreover, we tested the optimal spatial resolution for forest classification. The Random Forest Model was combined with predictive features derived from spectral reflectance, image texture, and vegetation coverage to map landcover types at four spatial resolutions. The results showed that the overall accuracy (OA) of four land-cover maps had a U-curve tendency with increasing spatial resolution. The 2 m Pléiades image generated the highest classification accuracy (Kappa=0.70, OA=0.77) among four types of images. The accuracy of three evergreen forest types also had a similar U-curve tendency. The ranges of the rate of identification (RI) were RI_CFF=68%-87%, RI_MPF=55%-84%, and RI_EBF=29%-74%. The CFF and MPF generated lower classification errors in terms of omission error (OE_CFF=0.26-0.46; OE_MPF=0.31-0.50) and commission error (CE_CFF=0.32-0.53; CE_MPF=0.31-0.46)compared with the EBF (CE_EBF=0.39-0.66; OE_EBF=0.47-0.71). Our results showed that the identification of forest types in subtropical regions is clearly subject to scale effects. Despite this, Landsat-8 imagery at 30 m resolution can produce the highest mapping precision due to its broader spectrum sensors. We proposed that the practical mapping of forest types in subtropical areas should consider the inherent trade-off between spectral features and spatial resolution of remote sensors rather than blindly pursuing high spatial resolution.

Spatial and temporal variation of vegetation water use efficiency and its response to meteorological factors in Sanjiang Plain.

SHI Xiao-liang, WU Meng-yue, ZHANG Na, DING Hao

2020, 39(5):  1651-1663. 

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Water use efficiency (WUE) is an important parameter for investigating the responses of terrestrial ecosystems to global change. It is of great significance to analyze the variation of WUE and its response to meteorological factors for research of carbon water cycling and regional scientific management of water resources. Based on MODIS GPP and ET remote sensing data, meteorological data and land cover data in 2000 and 2014, we analyzed the spatialtemporal change of vegetation WUE and the relationship between vegetation WUE and key meteorological factors in Sanjiang Plain. We further examined the change characteristics of WUE for each vegetation type in terms of land cover change. Annual mean variation of WUE in Sanjiang Plain showed a fluctuated decreasing trend. The mean annual vegetation WUE was 1.44 g C·kg^-1 H₂O. Monthly variation of WUE roughly showed a mono-peak curve. While WUE was lower from January to March and from November to December, it was higher in growing season (May to September). The seasonal WUE was highest in summer, followed by autumn, spring and winter. The intraannual change of WUE for each vegetation type showed a double peak curve, with the peak being mainly distributed in April-June and September. The averaged WUE values of different vegetation types ranked as mixed forest>coniferous forest>broadleaf forest>grassland>Cultivated land>permanent wetland. Vegetation WUE in Sanjiang Plain was positively correlated with precipitation, relative humidity and vapor pressure, but negatively correlated with temperature and sunshine hours. With the reduction of cultivated land area, the WUE of cultivated land increased by 11.1%. With the increased area of deciduous broadleaved forest and grassland, vegetation WUE increased by 12.8% and 15.9%, respectively.

Spatiotemporal evolution of NDVI and its seasonal response to climate change in the Loess Plateau from 1982 to 2015.

FAN Qian-qian, ZHAO An-zhou, WANG Jin-jie, ZHANG An-bing, PEI Tao

2020, 39(5):  1664-1675. 

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Based on data of GIMMS (Global Inventory Modelling and Mapping Studies) NDVI (Normalized Difference Vegetation Index), temperature, and precipitation, we analyzed the spatiotemporal variation of vegetation cover and its seasonal response to climate change in the Loess Plateau from 1982 to 2015, using the Ensemble Empirical Mode Decomposition (EEMD), linear regression analysis, and partial correlation analysis. In the interannual variation trend from 1982 to 2015, NDVI on the Loess Plateau increased significantly in the growing season, spring, summer, and autumn. The increasing rate of NDVI in each season also increased during 1982 and 2015, with the most obvious change in summer. Spatially, NDVI gradually increased from northwest to southeast in the growing season, spring, summer and autumn, which was statistically significant in most areas. As shown by the linear regression analysis, temperature had a significant increase trend in the growing season, spring, summer, and autumn, while precipitation increased in the growing season and autumn and decreased in spring and summer. The results of EEMD analysis further showed that in the growing season, spring, summer, and autumn, temperature first increased and then decreased, and precipitation first decreased and then increased. In terms of spatial variation, temperature had a significant increase trend in most areas during the growing season, spring, summer, and autumn, while precipitation had a significant increase trend only in some areas during autumn. There was a significant positive correlation between NDVI and temperature in the northeast and southwest of the Loess Plateau, and a significant positive correlation between NDVI and precipitation in the north and northwest of the Loess Plateau.

Spatial and temporal variations of reference evapotranspiration and its influencing factors in Guangxi Xijiang River Basin from 1965 to 2018.

YAN Yan, HUANG Kai-yan, HU Bao-qing, WANG Sheng, HUANG Yu-qing

2020, 39(5):  1676-1684. 

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Estimation of reference evapotranspiration (ET₀) could contribute to revealing water-heat balance and water cycle process and consequently provide reference for the sustainable utilization and exploration of regional water resources. Here, we re-fitted the net shortwave emissivity and calculated ET₀ in Guangxi Xijiang River Basin from 1965 to 2018, using improved Penman-Monteith model. The trend analysis and mutation point detection of ET₀ were performed by Mann-Kendall method. The spatialtemporal variations of ET₀ were analyzed by interpolation with inverse distance weighting method. Factors influencing ET₀ were determined based on the contribution rate of meteorological factors. At spatial scale, ET₀ presented an increasing tendency with decreasing altitude. The highest ET₀ values were mainly distributed in the central part of thebasin, while the lowest values occurred in the edge and slope zone of the YunnanGuizhou Plateau, which lies in the northwest part of the basin. ET₀ in spring varied with the longitude, while summer ET₀ showed a similar spatial pattern to that of the inter-annual ET₀. The mean annual ET₀ of the basin was 637.2 mm, with a declining rate of -0.018 mm·a^-1. The ET₀in spring, summer, winter and autumn were 0.053, -0.053, -0.007 and -0.011 mm·a^-1, respectively. ET₀ in all the seasons except spring showed an downward trend. The largest increase in ET₀ occurred in winter. The importance of dominant factors influencing ET₀ of the basin followed an order of relative humidity (with a contribution rate of 39.0%) > average wind speed (27.2%) > sunshine duration > average temperature. Relative humidity negatively affected ET₀, with a correlation coefficient of -0.673. Sunshine duration, average wind speed, and average temperature positively affected ET₀. The dominant driving factors of ET₀ and their contribution rates varied across different parts of the basin.

Interannual and monthly variations of catch per unit effort and the relation with sea surface temperature and chlorophyll concentration in fishing grounds (fishing area 48) of Antarctic krill.

ZHANG Ying-ying, XU Bo, ZHANG Heng, CHENG Tian-fei, YANG Sheng-long

2020, 39(5):  1685-1694. 

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Based on the catch of fishing season (January-June) and ocean remote sensing data of Antarctic krill fishing area from 2010 to 2015, we analyzed the spatiotemporal variations in the catch per unit fishing effort (CPUE) of Antarctic krill by using statistical method and yield center of gravity method. Results showed that the mean annual CPUE of Antarctic krill increased gradually from 2010 to 2015, with a peak in 2014 (18.6 t·h^-1). The mean monthly CPUE of Antarctic krill was lower in January (9.2 t·h^-1), while highest in May (20.9 t·h^-1). Nearly 60% of the catch times were in the summer period (January-March) near the South Shetland Islands. The Antarctic krill fishing grounds were concentrated in the sea area between 60°S-64°S and 46°W-62°W. The center of gravity in fishing ground shifted from the sea area near the South Shetland Islands to the northeast during January to June every year. Most of the fishing ground barycenter was mainly concentrated in the sea area near the South Shetland Islands. The optimum sea surface temperature (SST) of the fishing ground ranged from -1.8 to 1.9, -1.8 to 0.8 and 1.1 to 1.4 ℃ in fisheries subzones 48.1, 48.2 and 48.3, respectively. The optimum SST range of the high CPUE fishing areas from January to March was -0.8 to 1.2 ℃, which decreased from -1.8 to -0.4 ℃ in April-June period. The optimum ranges of chlorophyll a concentration in the subzones48.1, 48.2 and 48.3 were 0.09-1.21, 0.14-0.52 and 0.32-0.39 mg·m^-3, respectively. The chlorophyll aconcentration in the areas with high CPUE (>20 t·h^-1) values was 0.13-0.83mg·m^-3. Overall, the annual CPUE of Antarctic krill showed an increasing trend during 2010-2015. The main fishing area was located near the South Shetland Islands. The optimum SST range of the central fishing ground was -1.8 to 1.2 ℃, and the range of chlorophyll a concentration was 0.13-0.83 mg·m^-3.

Effects of cadmium on seed germination and seedling growth of different alfalfa varieties.

BAO Qiong-li, TANG Yi-ran, BAO Wan-kui, SONG Zheng-guo, HUANG Yi-zong

2020, 39(5):  1695-1705. 

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The effects of Cd²⁺ with different concentrations (0, 5, 10, 20, 50, 100, 200 mg·L^-1) on seed germination and seedling growth of seven alfalfa varieties were examined in a germination experiment with Petri dish filter paper. The results showed that germination indices of different alfalfa varieties were promoted by different extents with Cd²⁺ treatments in the range of 5-20 mg·L^-1. The fresh weight of Gannong No. 1 and Algonquin was significantly increased under 10 mg·L^-1 treatment. The inhibiting effects of Cd²⁺ treatments on the examined indices of different alfalfa varieties were greatly different. The germination potential of Empress, Amerigraze, Zhonglan No. 1 and Zhonglan No. 2 was significantly decreased under 5-200, 20-200, 50-200 and 200 mg·L^-1 treatments, respectively. The germination rates and germination indices of Zhonglan No. 1, Algonquin (Amerigraze), and Zhonglan No. 2 (Empress) were significantly reduced under treatments with Cd²⁺ concentration of 50-200, 100-200 and 200 mg·L^-1, respectively. Cd²⁺ concentration of 20-200 mg·L^-1 significantly decreased vigor index of all varieties. Fresh weight of all varieties significantly were decreased under treatments with Cd²⁺ concentrations of 50-200 mg·L^-1. All Cd²⁺ treatments significantly inhibited root and/or bud length of seven varieties. The correlations between germination rate, germination index, fresh weight and Cd²⁺ concentration were significant, with R² values being higher than 0.83. The tolerances of seven alfalfa varieties to Cd²⁺ stress, as evaluated comprehensively using the average value of subordinate function of all measurement indices, followed an order of Gannong No. 1 >Empress > Zhonglan No. 2 > Tianshui Alfalfa > Algonquin > Amerigraze > Zhonglan No. 1. In conclusion, the Empress, with high germination rate and tolerance to Cd²⁺ stress, could be recommended as potential candidate variety for the remediation of cadmium contaminated soil.

Toxic effects of river mercury contamination on early development of Oryzias latipes.

LIN Jing, YAN Hai-yu, JING Min, YANG Guang-hong

2020, 39(5):  1706-1717. 

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The Qingzhen chemical industry is an important source of Hg pollution to the Dongmenqiao River, Guizhou Province, southwest China. To evaluate the Hg pollution status of this river, we measured the concentration and distribution of Hg in environmental samples collected from the Dongmenqiao River. The average THg and MeHg concentrations were (135.79±47.40) and (0.64±0.58) ng·L^-1 in river water, (3.38±1.91) mg·kg^-1 and (10.47±0.40) μg·kg^-1 in biofilms, and (23.21±20.22) mg·kg^-1 and (32.74±10.96) μg·kg^-1 in sediments, respectively. To further clarify the risk of mercury on aquatic organisms in this river, embryosand larvae of Oryzias latipes were exposed to different treatments with Hg-ontaminated water, biofilms and sediments collected from the river. After 15 days of exposure, the hatching time of embryos was prolonged, the hatching rate was significantly decreased, and the mortality rate was significantly increased. The results showed the inability of embryos in breaking the membrane, yolk sac edema and other malformation effects, as well as different degrees of malformation of the newly hatched larvae. After 24 h, 48 h, 96 h, and 21 d exposure, the mortality and deformity rates significantly increased with the increasing time of exposure, and a series ofdeformity effects occurred mainly as spinal curvature. Our results indicated that mercury pollution in the Dongmenqiao River may significantly affect the early growth of O. latipes.

A review on crop straw returning to field: Effects, problems and countermeasures.

SONG Jia, ZENG Xi-bai, WANG Ya-nan, BAI Ling-yu

2020, 39(5):  1715-1722. 

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Crop straw returning to soil is one of the effective measures to improve soil physicochemical properties, enhance the activities of microorganisms and enzymes, and increase crop yield. It is one of the important ways of crop straw resource utilization. However, the straw returning to soil could lead to some negative impacts, such as decreasing germination rate of crops, increasing the occurrence of crop diseases and pests, and accumulation of soil heavy metals and other poisonous and harmful substances. The main way of crop straw returning to soil was the direct straw returning, while the indirect way of the crop straw returning to filed was composting. The decomposition rate and effect of the straw in soils mainly depended on the chemical composition of the straws (especially carbonnitrogen ratio), soil microbial status, soil temperature, and soil moisture. The future researches should focus on the methodologies of straw returning to soil, rapid decomposing agents and their application conditions, the impacts and control on the occurrence of crop diseases and pests of next season crops, the integration of agricultural machinery and agronomy, the ability to mitigate global change. Furthermore, we should improve methodologies and technologies related to straw returning to field and promote rapid application of crop straw returning to soil.

Research advances in underlying mechanism and modeling of dissolved organic carbon leaching in forests.

GUO Li-na, JIA Yu-xuan, LI Tong, LIU Kan, ZHANG Zhi-bo, XIE Jun-fei, SHI Sheng-wei

2020, 39(5):  1723-1733. 

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Leaching of dissolved organic carbon (DOC) is a key process in carbon cycling of terrestrial ecosystems. Forests are one of the main sources of DOC in terrestrial ecosystems. DOC can reach the bottom layer of soil through leaching, resulting in changes of organic carbon in the bottom layer of soil. The DOC in forest ecosystems enters water systems through surface runoff and groundwater seepage, and finally participates in marine carbon cycle. Therefore, exploring the underlying mechanisms of DOC leaching in forest ecosystems is of great significance for understanding key processes of global carbon cycle. Here, we reviewed the sources and sinks of DOC in forest ecosystems, and summarized several important underlying mechanisms of DOC leaching, including land use changes, climate change, acid deposition, atmospheric CO₂ increase, soil Fe-Al oxides. The advantages and disadvantages of empirical statistical models and process-based models for simulating DOC leaching and output fluxes were summarized. Considering the current status and shortcomings of DOC-related researches in forest ecosystems of China, we propose to establish a DOC leaching observation network across forest ecosystems in China to provide accurate and solid data for predicting DOC changes. Moreover, field observations, laboratory experiments, and model simulations should be combined to explore the underlying mechanisms of DOC leaching in forest ecosystems. It is necessary to strengthen the modeling of DOC leaching at typical regional and national scales in the context of environmental change.

Estimation of grassland net primary productivity in permafrost of Qinghai-Tibet Plateau based on machine learning.

LI Chuan-hua, SUN Hao, WANG Yu-tao, CAO Hong-juan, YIN Huan-huan, ZHOU Min, ZHU Tong-bin

2020, 39(5):  1734-1744. 

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There is still a great uncertainty in the estimation of net primary productivity (NPP). In this study, machine learning algorithm (RF and RBF-ANN) was used to estimate the NPP of grassland in permafrost of Qinghai-Tibet Plateau from 2002 to 2018. We analyzed the temporal and spatial pattern, variation characteristics, and response of grassland NPP to climate factors in the permafrost of Qinghai-Tibet Plateau. The results showed that: (1) The estimation results of machine learning are reliable and simple. (2) In the permafrost of Qinghai-Tibet Plateau, NPP showed a decreasing trend from southeast to northwest. The total NPP was 175.39 Tg C·a^-1, and the average NPP per unit area was 164.10 g C·m^-2·a^-1, showing a fluctuating trend. (3) The area with increased NPP accounted for 20.49% of the total area. The amplitudes of NPPincrease differed with grassland types, with an order of alpine wet meadow > alpine meadow > alpine steppe > alpine desert steppe. (4) Temperature was the dominant factor driving grassland NPP change in permafrost area of the Qinghai-Tibet Plateau. The influence of precipitation gradually weakened along the southeast to northwest.

Application of high resolution sensor in the study of plant water relations.

KANG Yun-peng, ZHANG Ping, HU De-chang, ZHU Jian-jun

2020, 39(5):  1745-1752. 

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The feasibility of a new type of humidity sensor in plant ecophysiological studies was evaluated. The features and parameters, necessary facilities associated with the sensor, the calibration and the ways of applications were investigated. Solutions to practical measurements were provided, with Ferula krylovii as an example. The results showed that the new type of humidity sensor exhibited features of high sensitivity, rapid response, good linearity, longtime stability, low dependence on temperature, low cost, and was applicable for continuous recording. Consequently, this type of humidity sensor provides an alternative way to measure humidity and transpiration in addition to the photosynthesis meters for researchers and students without access to the expansive equipment of photosynthesis measurement.

Screening of biocontrol bacteria against tomato wilt and the effect on defense enzyme activity of plants.

ZHOU Dong-xing, WANG En-ze, LIU Duo, JIN Cong-min, LI Xin, JIANG Shan, BAI Hao-tian

2020, 39(5):  1753-1760. 

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To select biocontrol bacteria for preventing tomato wilt, the gradient dilution coating method and the plate confrontation growth method were used for screening biocontrol bacteria from the worm cast and identifying the best strain. A pot experiment was carried out to examine the effects of the selected strain on tomato wilt and the activities of defense enzymes. The results showed that the bacteriostatic rate of DX-25 against Fusarium oxysporum was 66.09%, which was initially identified as Bacillus velezensis, with preventing rate being 59.25%±0.43% in pot. There were four treatments in the pot experiment: control (CK), F. oxysporum (KW), biocontrol bacterium DX-25 (DX), and pathogen+biocontrol bacterium DX-25 (D+K). The superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), lipoxygenase (LOX), chitinase (CHT) and β-1,3-glucanase (GLU) were used as the indicators for disease resistance in tomato, to investigate the effects of inoculation of biocontrol bacteria on defense enzyme activities in tomato plants. All treatments significantly increased the activities of these enzymes in stem. The D+K treatment enhanced the activities of PPO and GLU. The time for peak in activity of PPO and GLU in the combination of pathogen and biocontrol bacterium DX-25 strain was 48 h and 24 h earlier than that of single inoculation withF. oxysporum or DX-25, respectively. Our results showed that the combination of DX-25 and pathogens could induce a faster resistance response of tomato plants.